The present invention relates to apparatus for controlling the rotation of motors. More particularly, the invention relates to a motor rotation control apparatus so designed that the phase of a rotation signal of a frequency corresponding to the rotation speed of a motor is compared with the phases of a reference clock lock signal and thus the motor is controlled in accordance with the result of the comparison so as to make its rotational phase coincide with that of the reference clock lock signal.
Methods heretofore known for controlling the rotation of motors include a phase control method and a speed control method. The phase control method is one in which the phase of a rotational phase signal generated one per revolution of a motor is controlled to make it coincide with the phase of a reference clock signal, and the speed control method detects the rotation speed of a motor to control its rotation.
While the phase control method ensures a high degree of accuracy as compared with the speed control method, there is a disadvantage that during the starting of a motor the rise in the motor speed is slow and hence a considerable time is required from the start to a locking-in.
Recently, small electronic still picture cameras incorporating a magnetic disk type recorder have been proposed and it is desirable for this type of camera that the rotation of the disk is started through the half depression of the shutter button just before taking a photograph or any other means and the disk is stopped upon completion of the recording thereby reducing the electric power consumption due to the rotation of the disk. However, since naturally no picture can be recorded during the interval between the time that the rotation of the disk is started and the time that the desired rotation at which its phase coincides with the phase of the reference clock is attained (this is hereinafter referred to as a lock-in condition), the interval of time between the starting and the lock-in must be reduced as far as possible. For example, with a disk control apparatus for electronic still picture cameras, each time the rotation of the disk, which has previously been rotated and then stopped, is started again, the disk should preferably be controlled to properly adjust the phase reference to the disk. More specifically, where a picture for one field or frame is recorded on each track, while the phase reference need not necessarily be adjusted to the other tracks, the adjustment of the phase reference to the other tracks has the effect of diametrically aligning the vertical synchronizing signals of all the tracks. This has many advantages in that the desired lock-in condition is readily attained by the reproduced signal of the next track when switching from one frame to another during the reproduction and so on. Thus, the phase control should preferably be effected in such a manner that the phase reference of each track is adjusted to the other tracks, that is, the phase reference of the rotating object is adjusted every time in cases where the start and stop of the rotation of the rotating object are repeated a plurality of times.